Surface treatment of darc films to reduce defects in subsequent cap layers

ABSTRACT

The present invention comprises a method for preventing particle formation in a substrate overlying a DARC coating. The method comprises providing a semiconductor construct. A DARC coating is deposited on the construct with a plasma that comprises a silicon-based compound and N 2 O. The DARC coating is exposed to an atmosphere that effectively prevents a formation of defects in the substrate layer. The exposed DARC coating is overlayed with the substrate.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for treating depositedanti-reflective films, DARC films, to reduce defects in overlaying caplayers and to a device comprising a DARC film, the device having reduceddefects in a cap layer, overlaying the DARC film.

BACKGROUND OF THE INVENTION

[0002] Photolithographic techniques have wide use in fabrication ofsemiconductor devices, particularly in a fabrication of miniaturizedelectronic components. Photolithography processes comprise applying aphotoresist composition to a substrate material, such as a siliconwafer. Once applied, the photoresist is fixed to the substrate to form acomposite. The composite of substrate and photoresist is subjected to animage-wise exposure of radiation.

[0003] The radiation exposure causes a chemical transformation in theexposed areas of the photoresist covered surface. Visible light,ultraviolet (UV) light, electron beam and x-ray radiant energy areenergy sources in wide use in photolithography. After image-wiseexposure, the photoresist coated substrate is treated with a developersolution to dissolve and to remove either the radiation-exposed areas orthe unexposed areas of the photoresist.

[0004] One problem encountered when using photolithographic techniques,particularly in fabricating microcomponents, is back reflectivity orback reflection of light. Back reflection is a cause of thin filminterference and reflective notching. Thin film interference results inchanges in critical line width dimensions caused by variations in thetotal light intensity in the resist film as the thickness of the resistfilm changes. Reflective notching occurs when the photoresist ispatterned over substrates containing topographical features, whichscatter light throughout the photoresist film, leading to line widthvariations. In an extreme case, reflective notching forms regions withcomplete resist loss.

[0005] Antireflective coatings such as DARC coatings and BARC coatingshave been introduced into the photolithography process in order toreduce problems caused by back reflection. Antireflective coatingsabsorb radiation used for exposing the photoresist.

[0006] Substrate fabrication of semiconductor devices typically producesa number of surfaces comprised of dissimilar materials. Many of thesesurfaces do not have a uniform height, thereby rendering the waferthickness non-uniform. For example, as is shown in prior art FIG. 1, theheight of a material such as a boro-phosphosilicate glass (BPSG) layer12 of the wafer section 10, does not have the same height at points 14,16 and 18. Further, surfaces may have defects such as crystal latticedamage, scratches, roughness, or embedded particles of dirt or dust. Forvarious fabrication processes that are performed, such as lithographyand etching, unplanned non-uniformities in height and defects at thesurface of the wafer or at the surface of any layer of the wafer must bereduced or eliminated.

[0007] One problem encountered with the DARC coating arises when anitride layer or other type of layer is positioned in contact with theDARC coating. In particular, the problem arises when the layer overlaysthe DARC coating. It has been observed that the overlying layer, such asa silicon nitride layer, develops microparticles within the layer. Themicroparticles have a diameter of about 0.13 microns in the nitridefilm. The microparticles are formed as a result of one or more reactionsbetween the DARC coating and the overlying layer. The microparticles areundesirable because they distort the topography of the silicon nitridesurface or other capping surface as well as cause distortion at aninterface with the DARC coating as is illustrated at 10 in prior artFIG. 1. The distortion occurs because the thickness of the cap, such asthe silicon nitride cap, ranges from about 0.1- to- 0.2 microns, whichis within the diameter range of the microparticles.

[0008] One approach to preventing or eliminating surface discontinuitiesincludes taking action during fabrication in order to prevent surfaceheight discontinuities from occurring in the first place. The SasakiPatent, U.S. Pat. No. 5,226,930, which issued Jul. 13, 1993, describes amethod for preventing agglomeration of colloidal silica in a siliconwafer. The patent describes forming an aqueous colloidal silicondispersant from an aqueous sodium silicate solution and mixing atrialylhalosilane with the aqueous colloidal silicon dispersant to formtrialkylsilane. With this treatment, colloidal silica is substantiallyprevented from undergoing gelation during drying. This chemical reactionthen prevents a polishing slurry that includes colloidal silica fromcausing scratches or latent flaws on a wafer surface during polishing ofthe silicon wafers.

SUMMARY OF THE INVENTION

[0009] One embodiment of the present invention includes a method forpreventing particle formation in a semiconductor layer overlaying a DARCcoating. The method comprises providing a semiconductor construct. ADARC coating is deposited on the semiconductor construct. The DARCcoating is treated with a plasma under conditions that effectivelyprevent the formation of defects in a layer subsequently deposited ontop. The treated DARC coating is overlaid with the semiconductor layer.

[0010] Another embodiment of the present invention includes a method formaking a silicon nitride cap for a semiconductor device that has asubstantially uniform topography. The method comprises providing asemiconductor construct and depositing a DARC coating on thesemiconductor construct. The DARC coating is deposited with a plasmathat comprises SiH₄ and N₂O. The DARC coating is then treated with aplasma to prevent the formation of defects in a layer subsequentlydeposited on top. The DARC coating is overlaid with the silicon nitridecap.

[0011] One other embodiment of the present invention includes asemiconductor device. The semiconductor device comprises a DARC coatingand a layer overlaying the DARC coating. The overlaying layer issubstantially free of particles formed by one or more reactions with theDARC coating and the overlaying layer.

[0012] Another embodiment of the present invention includes a gatestack. The gate stack comprises a DARC coating and a layer overlayingthe DARC coating. The layer is substantially free of particles formed byone or more reactions with the DARC coating and the overlaying layer andhas a substantially uniform topography.

DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a cross sectional prior art view of one embodiment of agate stack with microparticle formation in a nitride layer.

[0014]FIG. 2 is a cross sectional view of one embodiment of a gate stackof the present invention, free from microparticles in a nitride cap.

[0015]FIG. 3 is a schematic view of one embodiment of an RF source forplasma formation used in the present invention.

[0016]FIG. 4 is a schematic view of one embodiment of an RF plasmagenerator used in the process of the present invention.

[0017]FIG. 5 is a schematic view of one other embodiment of an RF plasmagenerator used in the process of the present invention.

DETAILED DESCRIPTION

[0018] In the following detailed description of the invention, referenceis made to the accompanying drawings which form a part hereof, and inwhich is shown, by way of illustration, specific embodiments in whichthe invention may be practiced. In the drawings, like numerals describesubstantially similar components throughput the several views. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention. Other embodiments may be utilizedand structural, logical, and electrical changes may be made withoutdeparting from the scope of the present invention.

[0019] For purposes of this specification, the terms “chip”, “wafer” and“substrate” include any structure having an exposed surface ofsemiconductor material with which to form integrated circuit (IC)structures. These terms are also used to refer to semiconductorstructures during processing, and may include other layers that havebeen fabricated thereupon. The terms include doped and undopedsemiconductors, epitaxial semiconductor layers supported by a basesemiconductor or insulator, as well as other semiconductor structureswell known in the art. The term “conductor” is understood to includesemiconductors, and the term “insulator” is defined to include anymaterial that is less electrically conductive than the materialsreferred to as “conductors.” The following detailed description is,therefore, not to be taken in a limiting sense.

[0020] One embodiment of the present invention comprises a method forreducing small particle formation in a nitride film or other type offilm that overlays a DARC film or coating. The method includes treatinga surface of the DARC with an oxygen plasma or a nitrous oxide plasma ortreating the DARC surface with ammonia prior to overlaying the DARCcoating with the nitride film cap.

[0021] “DARC” as used herein refers to a deposited antireflectivecoating. The DARC material comprises, for example, a silicon-rich oxide,a silicon-rich nitride, or a silicon-rich oxynitride,Si_(x)O_(y)N_(z)(H) or Si_(x)O_(y)N_(z) or Si_(x)O_(y):H.

[0022] “Nitride” as used herein refers to silicon nitride, Si_(x)N_(y),such as Si₃N₄, or silicon oxynitride, Si_(x)O_(y)N_(z). Silicon nitrideis preferred for use in thin films because it is denser than silicondioxide. Silicon nitride films may be grown by an exposure of a siliconsurface to silicon-based gas such as SiH₄ or dichlorosilane, DCS, andammonia at a temperature of about 500 to 1200 degrees Centigrade.

[0023] “Semiconductor construct” or “semiconductor profile” as usedherein refers to a multi-layered article that has or that is capable ofhaving components of a semiconductor device. The multi-layered articleis in a stage of semiconductor device fabrication or is a completedsemiconductor device.

[0024] The DARC coating that is treated in the process of the presentinvention has a multiple functionality. In a photolithography process,the DARC coating aids in preventing undesirable light reflection duringa step of “setting” a photoresist. The DARC coating is also usable inpreventing profile distortion in photolithography fabrication. Inparticular, the DARC coating does not produce a problem of “footing” inmicrocomponents of semiconductors. This benefit is particularlyimportant in the fabrication of very small circuitry.

[0025] The DARC coating has been found to have desirablephotolithographic properties. The DARC coating is more reliable andproduces a larger process window with respect to circuit size than otherantireflective coatings such as a BARC coating.

[0026] The method of the present invention substantially preventsformation of the microparticles by “sealing” the surface of the DARCcoating through oxygen plasma treatment or nitrous oxide plasmatreatment or through an ammonia ambient heat treatment. It is believedthat when the DARC coating is treated with an oxygen plasma, a silicondioxide barrier is formed on the DARC surface. The silicon dioxidebarrier is substantially nonporous and is very hard.

[0027] An ammonia heat treatment produces a barrier on the DARC surfacethat is substantially silicon nitride, Si_(x)N_(y). The silicon nitridebarrier film is a good diffusion barrier. The silicon nitride barrier isformed by exposing the DARC coating to a silicon-based gas and ammoniaat a temperature of about 350 to 1200 degrees Centigrade. The DARCsurface treatment, oxygen treatment and ammonia treatment, are believedto render the DARC coating surface substantially non-reactive.

[0028] Embodiments of the present invention also include a semiconductorconstruct or profile that comprises a DARC coating and a capping layerthat overlays the DARC coating. The capping layer is substantially freeof microparticles and has, in one embodiment, a uniform surfacetopography. In another embodiment, the surface topography is as desired.

[0029] One embodiment of the process of the present invention issummarized in Table 1. The process includes deposition of a plasma thatcomprises SiH₄, to make the DAR coating. This step is summarized inTable 1 under “Deposition,” “Plasma On”, and “SiH₄.” A next stepcomprises exposure of the DARC coating to a nitrous oxide plasma or toan oxygen plasma or to an oxynitride plasma. The plasma source is, inone embodiment, a remote plasma source, such as is illustratedschematically at 58 in FIG. 4. An external radio frequency (RF) coilsuch as is illustrated at 42 in FIG. 3 may be used to generate theplasma gas. This step is designated in Table 1 under “Deposition” as“N₂O”, “Argon or Helium” and “RF Power.” With this plasma generationmethod, in one embodiment, an oxygen plasma field is generated at onelocation such as is shown at 60 in FIG. 4 and is transported downstreamto a wafer 62 containing a DARC coating. With this method, the plasma ismonitored for identification of plasma discharge, ionic recombination,and reduction of electron density. TABLE 1 Deposition RF Purge PhysicalPurge Plasma On Argon or He He or Argon Flow SiH₄ Plasma On Plasma OffN₂O RF Power > 0 Ar or He RF Power

[0030] In another embodiment illustrated at 70 in FIG. 5, a directplasma generating system 70 includes a chamber 72, a vacuum system 74,and a supply of oxygen or another oxygen source such as nitrous oxide,nitric oxide, or carbon dioxide 76. Wafers 78, 80, 82, and 84 comprisingprofiles with the DARC coating are loaded into the chamber 72. Pressurewithin the chamber 72 is reduced and a vacuum is established. Thechamber 72 is then filled with oxygen. A power supply creates a radiofrequency (RF) field through electrodes 86 and 88 in the chamber 72. TheRF field energizes the oxygen to make an oxygen plasma 90. In the plasmastate, the oxygen reacts with the surface of the DARC to make silicondioxide. Radial flow, inverse radial flow, and hot wall reactors mayalso be used to generate the plasma.

[0031] While a radio frequency induced glow discharge field isdescribed, it is believed that other oxygen plasma generating methodsmay be employed in the method of the present invention. The plasmasource may include, in other embodiments, microwave discharges, electroncyclotron resonance sources, high-density reflected electron, heliconwave, inductively coupled plasma, and transformer coupled plasma.Microwave excitation is applied by localized electron cyclotronresonance, surface wave and distributed electron cyclotron resonance.

[0032] One other type of RF plasma generation device is illustratedgenerally at 40 in FIG. 3. For this generation device, an induction coil42 is typically wound around a quartz tube 44 appended to one side of ametal vacuum cross-designed for substrate manipulation, and temperaturecontrol, shown schematically at 46. The mechanism by which power isimported to the gas stream is through an external inductor or externalcapacitor. The use of these external devices allows sharp resonant peakswith high Q values to develop in the RF circuit. High Q values producehigh fields and high circulating currents.

[0033] A process gas is introduced through a plasma tube at 48 where itis ionized and/or dissociated by the RF plasma. Operating pressures arein a range of 1 mTorr to 20 Torr. Reactive species, such as atomicoxygen generated by electron impact dissociation of oxygen gas, diffusefrom the plasma region to the substrate surface. Ions generated in theplasma-coil region are “thermalized” during transport from this regionto the substrate 50 located downstream from the RF coil 42. An afterglowextending from the plasma coil towards the substrate 50 is oftenobserved under typical pressure and power conditions.

[0034] In one embodiment directed to gate stack fabrication, externalinductors serve to couple RF power to the plasma gas through adielectric medium. External coupling eliminates contamination of thegate stack by the electrode material. In the remote RF process such asis illustrated at 50 in FIG. 4, a process gas such as oxygen or nitrousoxide is introduced at 52 or 54 through a plasma tube 56 where it isionized and /or dissociated by the RF plasma-generating device 58.Operating pressures for the remote process are typically in a range of 5to 100 mtorr. Operating pressures for the direct plasma generatingprocess range from 1 to 7 Torr.

[0035] In the remote plasma generation process, reactive species, suchas nitrous oxide or oxygen radicals, generated by electron impactdissociation of N₂O gas or oxygen gas, diffuse from a plasma region 60to a wafer substrate surface 62. Ions generated in the plasma coilregion 60 are “thermalized” during transport from this region to thewafer substrate located downstream from the RF coil. An afterglowextending from a plasma coil toward the substrate is often observedunder typical pressure and power conditions. Ions created outside theplasma coil region are not subjected to high E-fields and do not gainsignificant energy.

[0036] In the plasma generation process shown in FIG. 4, an inert gasplasma dissociates molecular nitrous oxide or oxygen or ammoniadownstream from an RF coil which is positioned schematically at 58. Anoble gas such as argon discharge or helium discharge acts as amechanism to couple energy through electrons, ions and metastables, intonitrous oxide or other oxide which is introduced downstream near thesample. Argon or helium or other inert gas or mixture of inert gases isadded to the process at 52 or 54. This indirect process minimizesinteractions of nitrous oxide or oxygen with a reactor wall 64 byminimizing the contact area of the nitrous oxide or oxygen with the wall64.

[0037] The plasma, mixed with argon or helium or other inert gas, isreduced in power and, consequently, in energy. The plasma is then purgedfrom the site of fabrication of the DARC coating. Once treated, the DARCcoating is overlaid with a silicon nitride film.

[0038] In one embodiment illustrated at 20 in FIG. 2, the method of thepresent invention is used to fabricate a component such as a gate stack.The gate stack includes a bottom silicon field oxide layer 22. Apolysilicon layer 24 overlays the field oxide layer. The polysilicon is,in one embodiment, deposited on the field oxide 22 at a temperature ofabout 500 to 650 degrees Centigrade. The deposition may take place witha gas stream that is one-hundred percent silane or with gas streamscomprised of nitrogen or hydrogen or oxygen or combinations of thesematerials. The polysilicon layer 24 may have an order ranging fromamorphous to columnar polycrystalline silicon. The use of hydrogen gastends to reduce grain size. Dopants may be added as appropriate forspecific applications.

[0039] The polysilicon layer 24 is overlaid with a layer of tungstensilicide 26. The tungsten silicide layer acts as a dielectric. Thetungsten silicide layer is formed by deposition of WF₆ gas with SiH₄ toform WSi₂. The deposition occurs, in one embodiment, in a chemical vapordeposition, CVD, method.

[0040] The tungsten silicide layer 26 is overlaid by the DARC coating30. The DARC coating 30 is also deposited and is then exposed to a gasstream that comprises oxygen or nitrogen or ammonia or N₂O plasma inorder to “inactivate” the surface of the DARC coating. The gas stream ismixed with argon gas or other inert gas such as helium.

[0041] Once the DARC coating is deposited, an RF purge is performed. TheRF purge is performed in the presence of argon or helium or other inertgas and in the presence of plasma. With the RF purge, the DARC coatingis exposed, in one embodiment, to a plasma of oxygen and argon or heliumor other inert gas. This step is designated in Table 1 as the “RFPurge.” The RF purge is followed by a purge whereby a flow of argon gasor helium gas or other inert gas is continued and the plasma supply isstopped.

[0042] A silicon nitride layer 28 overlays the DARC coating 30. Thesilicon nitride layer 28 caps the gate stack 10. The silicon nitridelayer 28 has a thickness of 0.1 to 0.2 microns. The silicon nitride maybe deposited by a conventional LPCD or by a plasma enhanced chemicalvapor deposition, PECVD.

[0043] Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptions or variations of the present invention.Therefore, it is manifestly intended that this invention be limited onlyby the claims and the equivalents thereof.

In the claims:
 1. A method for preventing defect formation in asemiconductor layer overlaying a DARC coating, comprising: providing asemiconductor construct; depositing a DARC coating on the semiconductorconstruct; exposing the DARC coating to an atmosphere that effectivelyprevents a formation of defects in the semiconductor layer; andoverlaying the exposed DARC coating with the semiconductor layer.
 2. Themethod of claim 1 and further including energizing the atmosphere priorto exposing the DARC coating to the atmosphere.
 3. The method of claim 2wherein the atmosphere is energized to make a plasma.
 4. The method ofclaim 3 wherein the plasma is made with a radio frequency energy source.5. The method of claim 2 wherein the atmosphere is energized with heat.6. The method of claim 1 wherein the DARC coating is deposited on ametallized layer.
 7. The method of claim 1 and further includingproviding a plasma comprising SiH₄ and N₂O to make the DARC coating. 8.The method of claim 1 and further including purging the atmosphere priorto overlying the DARC coating.
 9. The method of claim 1 wherein theatmosphere is energized substantially concurrently with contact with theDARC coating.
 10. The method of claim 1 wherein the atmosphere isenergized prior to contact with the DARC coating.
 11. The method ofclaim 1 and further including diluting the atmosphere with an inert gas.12. The method of claim 1 and further including adding oxygen to theatmosphere to make an oxygen plasma.
 13. The method of claim 1 andfurther including adding ammonia to the atmosphere.
 14. A method formaking a silicon nitride cap for a semiconductor device that has asubstantially uniform topography, comprising: providing a semiconductorconstruct; depositing a DARC coating on the semiconductor construct;exposing the DARC coating to an atmosphere that effectively prevents aformation of defects in the silicon nitride cap; and overlaying the DARCcoating with the silicon nitride cap.
 15. The method of claim 14 andfurther including energizing the atmosphere prior to exposing to theDARC coating to the atmosphere.
 16. The method of claim 15 wherein theatmosphere is energized to make a plasma.
 17. The method of claim 16wherein the plasma is made with a radio frequency energy source.
 18. Themethod of claim 15 wherein the atmosphere is energized with heat. 19.The method of claim 14 wherein the DARC coating is deposited over ametallized layer of the semiconductor device.
 20. The method of claim 14and further including purging the atmosphere prior to overlying the DARCcoating.
 21. The method of claim 14 wherein the atmosphere is energizedsubstantially concurrently with the DARC coating.
 22. The method ofclaim 14 wherein the atmosphere is energized prior to contact with theDARC coating.
 23. The method of claim 14 and further including dilutingthe atmosphere with an inert gas.
 24. The method of claim 14 and furtherincluding adding oxygen to the atmosphere to made an oxygen plasma. 25.The method of claim 14 and further including adding ammonia to theatmosphere.
 26. A semiconductor device, comprising: a DARC coating; anda layer overlaying the DARC coating, the layer substantially free ofparticles formed by one or more reactions with the DARC coating and theoverlaying layer.
 27. The semiconductor device of claim 26 wherein thelayer overlying the DARC coating has a substantially uniform topography.28. The semiconductor device of claim 26 wherein the layer overlying theDARC coating comprises silicon nitride.
 29. The semiconductor device ofclaim 26 wherein the DARC coating comprises a silicon nitride or siliconoxynitride selected from the group consisting of Si_(x)O_(y):H,Si_(x)O_(y)N_(z)(H), Si_(x)O_(y)N_(z) and Si_(x)N₄.
 30. Thesemiconductor device of claim 26 wherein the DARC coating comprisesSi_(x)N₄ wherein x is greater than
 3. 31. The semiconductor device ofclaim 26 and further including a layer underlying the DARC coating. 32.The semiconductor device of claim 31 wherein the layer underlying theDARC coating comprises tungsten silicide.
 33. A gate stack, comprising:a DARC coating: a layer overlaying the DARC coating, the layersubstantially free of particles formed by one or more reactions with theDARC coating and the overlaying layer.
 34. The gate stack of claim 33wherein the layer overlying the DARC coating comprises silicon nitride.35. The gate stack of claim 33 wherein the layer overlying the DARCcoating has a substantially uniform topography.
 36. The gate stack ofclaim 33 and further comprising a layer that underlies the DARC coating.37. The gate stack of claim 36 wherein the layer that underlies the DARCcoating comprises tungsten and silicon.
 38. The gate stack of claim 36and further comprising polysilicon that underlies the layer thatunderlies the nitride cap.
 39. The gate stack of claim 38 and furthercomprising a silicon layer that underlies the polysilicon.